I found this cool timeline feature at the Metropolitan Museum of Art, the Heilbrunn Timeline of Art History. It is awesome from a teacher's standpoint as things to use in class. But it also has some great information on various presidential artwork. I found this great article on George Washington and his image:
The multiplicity of depictions of George Washington (1732–1799) testifies to his persistence in American life and myth. During his lifetime, his very image, whether presented as a Revolutionary War hero or as chief executive of the United States, exemplified the ideal leader: authoritative, victorious, strong, moral, and compassionate. Over the course of the nineteenth century, American and European popular culture elaborated on Washington's iconic persona and adapted it to patriotic and sentimental purposes.
...The extraordinary outpouring of emotion after Washington's death on December 14, 1799, reverberated worldwide, as mourners grieved not merely for the man himself but for the hero he had become and, still more warmly, for the father of the country. Washington's role in American life had been of long duration and great depth. His image symbolized the power and legitimacy of the newly independent nation, which was still very much in the formative stages during the nineteenth century. His imposing figure as president embodied ideals of honesty, virtue, and patriotism. Nineteenth-century images of Washington ranged from his godlike apotheosis to scenes of his personal life. His home, Mount Vernon, on the Potomac River in northern Virginia, became a shrine to his mythic celebrity. In 1853, the Mount Vernon Ladies' Association was founded, mostly through the efforts of women, in order to save the historic property and honor Washington's legacy.
You can also find specific art pieces of Washington in this timeline and more information on them. For instance, this miniature of Washington:
This Irish miniaturist and goldsmith worked in Dublin, London, and Halifax before coming to America in 1775. He moved to New York in 1777 in search of portrait commissions and quickly became the miniaturist of choice, a distinction he held for more than fifteen years. His work is characterized by a rich palette, delicate brushwork, and fine hatching that meticulously delineates his sitters' features. In 1789, the new president, George Washington, sat for him in New York (then the U.S. capitol) and Ramage painted at least three miniatures, including this one, each in his characteristic elliptical form with his own, handmade scalloped cases.